Timing circuit



y 14, 1957 w. c. STRUVEN 2,792,535

TIMING CIRCUIT Filed Aug. 27, 1955 C0 1 m "3 rq I W x it E Q WW\/l! W I m KO N) INVENTOR.

WARREN C. STRUVEN med/M ATTQRNEY.

United States PatentO TIMING cracurr Application August 27, 1953, Serial No. 382,500 4 Claims. (Cl. 317-142) The present invention relates to an improved timing circuit adapted to produce a timed sequence of events in response to a trigger signal and including means precisely. controlling the operating time or duration.

Both mechanical and electrical timing means are well known and widely employed; however, conventional tirning means do not provide highly accurate timing control for both long and short operating periods. Electronic timers provide very accurate time delays or operating periods of short duration but operate with reduced accuracy for longer timing periods. The present invention is adapted to produce a precisely controllable operating period from a small fraction of a second to a number of seconds with an equally high degree of accuracy for either short or long periods.

It is an object of the present invention to provide an improved timing circuit.

Itis another object of the present invention to provide a timing circuitoperating with great accuracy for either short or long periods.

Numerous other advantages and possible objects of the invention will become apparent to those skilled in the art from the following description of a preferred embodiment of the invention taken together with the accompanying drawing wherein the sole figure is a circuit diagram of the invention.

Considering now the elements and connections of the illustrated embodiment of the invention and referring to the drawing, there are provided input terminals 11, of which one may be grounded, and which are adapted to have impressed thereon a trigger signal preferably in the form of a square wave voltage pulse that may be of very short duration. The ungrounded pole of the input terminals is connected to the control electrode 12 of a pentode vacuum tube 13 which has its cathode grounded through a resistor 14 so that the input pulse is applied between the control electrode and cathode of the tube 13 to control the conductivity thereof Plate voltage for the tube 13 is obtained from a positive bus 16adapted for connection to appropriate power supply means, and a plate resistor 17 is connected in series with the operating coil or" a fast acting relay 18 between the bus 16 and the plate electrode of the tube 13. The suppressor grid of the tube 13 is tied directly to the tube cathode, andthe screen grid is connected to the positive bus 16 through a resistor and to the cathode through a capacitor, in aconventional manner.

There is provided another vacuum tube 19 (in this case a three element tube) which is operatively connected with its cathode tied directly to the cathode of the first tube 13 and the anode connected through a plate resistor 21 to the positive bus 16. The anode of the second tube 19 is. also connected through a parallel resistoncapacitor combination 22 to the control electrode 12 of the first tube 13 and this control electrode 12 is connected through a variable resistor 23 to a negative bus. 24 ,that is, in turn, adapted for connection to the negative terminalof a power supply (not shown).

Patented May 14, 1957 ice There are provided in addition to the above-noted circuit elements a time delay circuit connected between the negative bus 24 and a second positive bus 26 adapted for connection to the positive terminal of a power supply (not shown). The voltage level of the two buses 24 and 26 is maintained at equal values and opposite polarities as, for example, at plus and minus volts so that the voltage of the time delay circuit swings equally about ground potential. A variable resistor 27 is connected to the second positive bus 26 and a pair of resistors 28 and 29 are connected in series therewith to the control electrode of the vacuum tube 19. A resistor 31 is connected at one end to the negative bus 24 and at the other end to one terminal 32 of a single pole double throw switch 33 having another terminal 34 connected to the juncture of resistors 28 and 29. The switch 33 is relay operated from the relay actuating coil 18 and the movable switch contact 35 thereof is connected through a capacitor 36 to the cathodes of the vacuum tubes 13 and 19 so that the capacitor 36 is alternately connectible to switch terminals 32 and 34 in response to operation of the relay coil 18.

In the illustrated embodiment of the invention, timed switching is the end result and this switching is produced by a relay operated single pole double throw switch 37 having a pair of terminals 38 and 39 individually connected to electrical leads 41 and 42 respectively and a movable contact 43 connected to a third electrical lead 44. Operation of the relay thus moves the switch contact 43 between switch terminals 38 and 39 so that the electrical lead 44 is successively connected to electrical leads 41 and 42 in response to energization of the relay coil 18 and any desired circuits may be connected to the electrical leads switched in this manner.

With regard to the operation of the invention, it is first noted that vacuum tube 13 is normally nonconducting because of the negative control grid bias and vacuum tube 19 is normally conducting because of the positive control grid bias. Impression of a positive voltage pulse at the input terminals 11 drives the control electrode 12 or" the first vacuum tube 13 positive with respect to the cathode thereof so that the tube conducts and draws current through the relay coil 18 in the plate circuit of the tube. As the tube conducts a current also flows in the cathode resistor 14 of the who so that the cathode potential rises an amount equal to the voltage drop across this resistor. As the cathode of the second vacuum tube 19 is directly connected to the cathode of the first vacuum tube 13 the cathode potential of the second tube also rises and this increased cathode potential is greater than the steady state positive control grid bias so that the cathode becomes positive with respect to the grid and the tube ceases to conduct. As tube 19 is cut off, current ceases to flow through the plate resistor 21 so that the plate potential rises to that of the positive bus 16 and this increased positive potential is coupled through the resistor-capacitor combination 22 to the control electrode 12 of the first vacuum tube 13. As long as the second tube 19 remains nonconducting, the positive plate potential thereof holds the control electrode of the tube 13 positive so that the first tube continues to conduct despite termination of the input pulse at terminals 11.

Conduction of the first vacuum tube 13 causes ha current flow in the plate circuit thereof through the relay coil 18. Normal position of the relay switches 33 and 37 connects the capacitor 36 to the negative bus 24 through the resistor 31 and connects electrical leads 42 and 44 together, as illustrated. Energization of the relay coil 18 by current fiow therethrough moves both switches 33 and 37 into operated poistions wherein capacitor 36 is connected to the control electrode of the second vacuum tube 19 and conductor 44 is connected to lead 41 instead of lead 42. Actuation of switch 33 causes movable contact 35 thereof to move into engagement with the upper fixed contact 34 so that the negative potential of capacitor 36 is applied through resistor 29 to maintain the grid of the second tube 19 negative with respect to the cathode thereof whereby the tube is maintained in a nonconducting state. The capacitor 36 is not only connected to the control electrode of the second vacuum tube 13 but is also connected through resistors 27 and 28 to the second positive bus 26 so that the negative capacitor charge is dissipated by current fiow therethrough from the positive bus 26. The time required to raise the capacitor potential (and thus in this case the grid potential) to the point where the tube fires, substantially ground potential, is determined by the time constant or resistance-capacitance product of this circuit. The resistance value may be varied by adjusting the variable resistor 27 so that a desired time delay is produced between the time that the second vacuum tube is cut off by application of the negative capacitor potential to the control electrode thereof and the time that said tube is again rendered conducting by the application of a sufficiently positive potential to the grid thereof. As the second vacuum tube conducts the plate current flowing through the plate resister produces a voltage drop to decrease the plate potential of the tube and this reduced potential then falls to overcome the negative potential applied through resistor 23 to the control electrode of the first tube 13 so that same is cut ofi. Cessation of conduction of the first tube 13 tie-energizes the relay coil 18 so that the switches 33 and 37 revert to normal position, as illustrated, and the circuit is again ready to receive an input pulse.

It will be seen that the delay time or period of actuation of the circuit is readily controllable from a very short to a very long duration and further that the period of actuation is very precisely controllable. It may be further noted that the input pulse must have a duration long enough to insure energization of the relay coil 13 and very fast relays are employed which only require current flow therethrough for about two millisecond to actuate the relay and thus input pulses having a sufiicient amplitude and a duration in excess of two millisecond will trigger the circuit and cause same to undergo one cycle of operation. It will also be appreciated that the time delay circuit is connected between voltages of equal value and opposite polarity so that the potential of the control electrode of the second vacuum tube swings about ground potential and thus the actual voltage values of the positive and negative buses 26 and 24 do not aifect the time delay.

Solely for the purpose of illustration there follows a list of-possible relative values of circuit elements of the invention.

Part Description Tubes 18 and 19 Type 6X8 Triode-Pentode. 14 1 kilohm.

25 lrilolun. 30 kilohm.

R =160 kilohrn, =39 micromicrofarad. 250 kilohm total.

1 megohm total.

39 kilohm.

68 kilohm.

2.2 kilohm.

36 3 microl'arad.

Cir

controlled energization thereof, a second normally conducting vacuum tube connected to said first tube for operation in response thereto and being connected to impress an output signal thereof upon the control electrode of said first tube for controlling conduction of said first tube, and a time delay circuit including power supply means connected between the control electrode and cathode of said second vacuum tube by the second switching means of said relay whereby said second tube is rendered nonconducti-ng for a predetermined period by relay actuation of said switching means by conduction of said first tube and said relay remains actuated for said period.

2. An improved timing circuit comprising first and second vacuum tubes having control electrodes and being coupled together for alternate conduction with the first tube thereof adapted to receive an input signal, a fast acting relay having a coil connected in the plate circuit of the first of said tubes and a pair of switching means of which one is adapted for switching extemal circuits, said switch means having first and second posi tions corresponding to relay coil normal and operated conditions, positive and negative electrical buses having voltages of equal amplitudes and of opposite polarity, a variable resistor connected from the positive bus to the control electrode of the second of said vacuum tubes, and a capacitor connected to the cathode of the second vacuum tube and through the other of said relay switching means to the negative bus in said first switch position and to the control electrode of the second tube in the second switch position whereby in response to an input signal said capacitor is disconnected from said negative bus and connected to the control electrode of one of said vacuum tubes for discharge through said variable resistor at a controlled rate to control the period of relay energization and thus the switching period for external circuits connected to one of the switching means of said relay.

3. A timing circuit comprising a first normally nonconducting vacuum tube having control means adapted to receive positive trigger voltages, a relay having an actuating coil connected in circuit with said first tube and switch means actuated by said coil, a second vacuum tube having a plate resistor and biased control means maintaining said tube normally conducting, a cathode resistor common to both first and second tubes, means coupling the plate of said second tube to the control means of said first tube, and a resistance-capacitance circuit including power supply means negatively charging the capacitance thereof and connected to control means of said second tube by the switching means of said relay upon coil energization thereof for maintaining said second tube nonconducting for a predetermined period and thereby maintaining said first tube conducting for a like period.

4. A timin circuit comprising first and second vacuum tubes having a common cathode resistor and separate plate resistors, negative bias means coupled to control means of said first tube to maintaining same normally nonconducting, an input terminal coupled to control means of said first tube and adapted to receive positive voltage pulses whereby said first tube is thereby rendered conducting, a relay having a coil connected in circuit with said first tube for energization by tube conduction and including first and second switches with the former adapted for switching external circuits, said relay switches having first and second positions corresponding to energized and die-energized coil conditions respectively, a positive potential source resistively coupled to control means of said second tube for ma ntaining same normally conducting, a negative potential source, a capacitor connected to the cathode of said second tube, said second contacts of said relay alternately connecting said capacitor to said negative potential source in the second switch position and to the control means of said second tube in the first switch position in response to relay actuation References Cited in the file of this patent UNlTED STATES PATENTS Bereskin July 2, 1940 6 Moe Aug. 13, 1946 Hayes et a1. Jan. 6, 1948 Hills Dec. 27, 1949 Bivens May 8, 1951 

